This invention relates to coating compositions for tablets. More particularly this invention relates to tablet coating compositions which can be applied in thin layers, are impervious to heat and which result, as desired, in tablet coatings which are either water soluble or are only soluble in the small intestine.
In addition to the sugar coatings for dragees, which have been known for many years, recently several synthetic resin coating agents for tablets have been developed which in comparison with dragees, have the advantage that a satisfactory coating for tablets can be obtained with substantially less and thinner layers. Depending on the nature of the synthetic resins used, there are obtained coatings which are either water soluble or are resistant to gastric juices (cf. German Pat. Nos. 1,056,786 and 1,228,757).
A disadvantage of these synthetic resin coatings is that they have to be applied to the tablet cores in the form of their solutions in organic solvents, such as, for example, acetone, alcohol, chloroform, carbon tetrachloride and the like. Although these solvents evaporate very readily and, therefore, the finished coatings are obtained in a comparatively short period of time, these coating agents possess many significant disadvantages. These disadvantages include the following:
1. Large amounts of solvents are needed as the solids content in these coating agents usually cannot be much more than 20% due to the viscosity requirements; PA1 2. The solvents, which are expensive in comparison with water, are either completely lost or can only be recovered by the use of very expensive apparatus; PA1 3. Because of the toxicity of the solvent vapors, special safety measures must be provided in the working areas in order to protect personnel; PA1 4. Most organic solvents are inflammable and mixtures of solvent vapors with air are explosive so that it is necessary to use expensive apparatus which is secure against possible fire and explosion.
In German Pat. No. 1,229,678, it has been proposed to apply molten polyethylene glycol to pre-heated tablet cores. This process admittedly avoids the use of solvents but then it necessitates the preparation of hot melts. Temperatures of up to 130.degree.C are unusually high for use in the production of tablet coatings. All tubes, spray nozzles and the like of the involved apparatus, must be heatable in order to avoid a solidification of the polyethylene glycol inside of or on the surfaces of the apparatus.
Furthermore, the tablets have to be pre-heated which is something to be avoided, if possible, particularly in the case of heat sensitive active materials. A further disadvantage of this process is the fact that it can only be carried out with the use of the polyethylene glycols which, as are known, have a particularly unpleasant taste.
It is accordingly an object of the invention to provide a new field of tablet coating composition which can be applied in thin layers, are impervious to heat and which as desired, can either be water soluble or only soluble in the medium found in the small intestine.
It is another object of the invention to provide a method of producing tablet coating compositions of the character indicated.
A further object of the invention is to provide synthetic resin tablet coatings which do not require the use of organic solvents in either their preparation or deposition.
Still another object is to provide synthetic resin tablet coatings compositions which can be applied at room temperature and in fairly high concentrations, i.e., coating compositions which can be easily and simply applied to tablet cores.
Other objects and various features of novelty and invention will be pointed out or will occur to those skilled in the art from a reading of the following specification.